Abstract
For understanding the physics of energetic particles, the deuterium experimental campaigns started in Large Helical Device (LHD) from March 2017. To investigate the behavior of energetic particles, a Fast-ion D Alpha (FIDA) diagnostic was installed on the LHD. In the FIDA diagnostic, the Doppler-shifted D alpha light from fast-neutrals are utilized as signals of energetic particles, where these fast-neutrals are produced by the charge exchange process between fast-ions in the plasma and actively injected neutrals by neutral beam (NB). The advantages of the FIDA diagnostic are the velocity and the spatially resolved measurement of fast-ions at the crossing point between its line of sight (LOS) and the incident line of NB. The most recent FIDASIM is enhanced to simulate signals produced in three-dimensional magnetic configurations. The new version of FIDASIM uses the fast-ion distribution function produced by GNET as input to simulate FIDA signals at LHD. In order to validate the new version of the code, measurements of radial profiles of fast-ions using the FIDA diagnostic are performed in magnetohydrodynamic (MHD)-quiescent plasmas. The measured spectra are in good agreement with the theoretical prediction by 3D-supporting FIDASIM at the center of the plasma (R= 3.5 m∼3.7 m, reff/a99= −0.28∼0.05) on the LHD when the line averaged electron density is ne_avg < 1.23 × 1019 m−3. On the other hand, the measured spectra are in disagreement with the theoretical prediction by 3D-supporting FIDASIM at even the center of the plasma when the line averaged electron density is ne_avg ≥ 1.23 × 1019 m−3.
Highlights
A magnetic confinement fusion reactor requires the sustainment of a high-temperature and highdensity plasma by energetic alpha particles from fusion reactions
The measured spectra and the predicted spectra are in good agreement between 654 nm to 659 nm at all measurement positions; this indicates that the halo and injected beam emission are accurately modelled
The Fast-Ion D Alpha (FIDA) diagnostic results and the FIDASIM results are in good agreement in MHD-quiescent plasmas at the center of the plasma for co-injection
Summary
A magnetic confinement fusion reactor requires the sustainment of a high-temperature and highdensity plasma by energetic alpha particles from fusion reactions. It is important to understand the behavior of energetic particles (such as fast-ions provided by plasma heating devices and fusion reactions) in magnetic confinement devices. The study of energetic particle confinement has advanced in tokamak type devices [1], and is one of the main topics in ITER [2]. The energetic particle confinement study in helical devices is rapidly developing. In the past several years, the fast-ion confinement study in helical devices demonstrated the potential for alpha particle confinement [7,8,9].
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